From a CNS article
As for Pope Benedict’s use of older, much taller miters, Msgr. Marini said they are a sign of how the church moves forward in history without ignoring or forgetting its past.
“Just as in his documents, a pope cites the pontiffs who preceded him in order to indicate the continuity of the church’s magisterium, so in the liturgical sphere, a pope uses the vestments and sacred furnishings” of previous popes, demonstrating a continuity in prayer, he said.